I'll try to give youan example:

Form name = FormName
List Box 1 Name - ListBox1
List Box 1 Row Source : Select Field1 From TableName1

List box 2 need to be filtered by the selection on ListBox1

List Box 2 Name - ListBox2
List Box 2 RowSource: Select FieldName From TableName2 Where Field1 =
Forms![FormName]![ListBox1]

In the OnClick event write the code
Me.[ListBox2].Requery
==========================
To go to the OnClick event:
1. open the form in design view
2. From the menu select view > properties
3. Select ListBox1 (click with the mouse on it), in the properties box
you'll see the properties of the list box
4. Find the OnClick property or After Update property, locate the cursor in
it.
5. On the right you'll see a button with three dots, click on it, and select
code view
6. Between the

Sub ...
   write the requery here
End Sub
==========================
I hope that example will give you a good start.